BPG4 regulates chloroplast development and homeostasis by suppressing GLK transcription factors and involving light and brassinosteroid signaling

Chloroplast development adapts to the environment for performing suitable photosynthesis. Brassinosteroids (BRs), plant steroid hormones, have crucial effects on not only plant growth but also chloroplast development. However, the detailed molecular mechanisms of BR signaling in chloroplast development remain unclear. Here, we identify a regulator of chloroplast development, BPG4, involved in light and BR signaling. BPG4 interacts with GOLDEN2-LIKE (GLK) transcription factors that promote the expression of photosynthesis-associated nuclear genes (PhANGs), and suppresses their activities, thereby causing a decrease in the amounts of chlorophylls and the size of light-harvesting complexes. BPG4 expression is induced by BR deficiency and light, and is regulated by the circadian rhythm. BPG4 deficiency causes increased reactive oxygen species (ROS) generation and damage to photosynthetic activity under excessive high-light conditions. Our findings suggest that BPG4 acts as a chloroplast homeostasis factor by fine-tuning the expression of PhANGs, optimizing chloroplast development, and avoiding ROS generation.

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Arabidopsis mutants used in the current study are available from the corresponding author.All the unprocessed data, gels, and blots were available within the paper and its Supplementary Information, and provided in the Source Data file.Source data are provided in this paper.
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All phenotype analysis, qRT-PCR analysis, observation for confocal laser scanning microscopy images, Y2H, BiFC, EMSAs, transient assay, GUS staining, visualization of ROS, and measurement of photosynthetic activity were repeated at least twice independently with similar results.
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Transgenic plants were selected by by resistance to to antibiotics.Genome-edited plants plants were selected by by by sequencing.sequencing.T-DNA inserted lines were selected by by PCR genotyping.
Real Time System (takara) was used to to quantitatively measure mRNA level.LAS-4000 mini (fujifilm) was used for chemiluminescence detection during western blot.ChemiDoc TouchTM Imaging System (BIO-RAD) was used for EMSAs.SpectraMax i3x and SpectraMax iD5 (MOLECULAR DEVICES) was used to to detect luciferase signals.LSM700 microscope (Zeiss) was used for Confocal laser scanning microscopy.FluorCam 800MF (Photon Systems Instruments) was used for measuring the Fv/Fm value.nature portfolio | reporting summary April 2023 dual use research of concern Hazards Could the accidental, deliberate or reckless misuse of agents or technologies generated in the work, or the application of information presented in the manuscript, pose a threat to: therapeutically useful antibiotics or antiviral agents Enhance the virulence of a pathogen or render a nonpathogen virulent Increase transmissibility of a pathogen Alter the host range of a pathogen Enable evasion of diagnostic/detection modalities Enable the weaponization of a biological agent or toxin Any other potentially harmful combination of experiments and agentsA rabbit polyclonal antibody against BPG4 (anti-BPG4 antibody) was generated in this study, using the MBP-BPG4 recombinant protein.Anti-ACTIN antibody (0869100-CF, MP Biomedical) Anti-Myc antibody (9E10, Sigma Aldrich) Anti-GFP antibody (A11122, Molecular Probes) Anti-rabbit horseradish peroxidase-conjugated secondary antibody (W4018, Promega) Anti-mouse horseradish peroxidase-conjugated secondary antibody (W4028, Promega) normal rabbit IgG (Dako, Glostrup, Denmark, #X0936) Donkey anti-rabbit IgG secondary antibody, Alexa Fluor™ Plus 647 (Invitrogen #A32795, 1:200 dilution) bpg4-1D bpg4-1D was was screened screened in in in in FOX FOX line.line.bpg4-1 and bpg4-2 were isolated in in ABRC T-DNA insertion lines.